New 'Mutant Enzymes' Could Solve Earth's Plastics Problem

Scientists accidentally created an enzyme that can break down plastic. But is it any better than recycling?

You might call it a happy accident: As environmentalists urge the world to address the plastic pollution crisis, a team of researchers has unwittingly engineered an enzyme that may, one day, literally eat our troubles away.

Biologists at the U.K.’s University of Portsmouth were studying the structure of an enzyme that can break down polyester when they found a way to tweak it. The result, according to a study published this week in the Proceedings of National Academy of Sciences, is a “mutant enzyme” that can degrade plastics 20 percent more efficiently than its original form.

The enzyme comes from a bacteria, Ideonella sakaiensis 201-F6, which was discovered in 2016 by Japanese researchers, who subsequently found that it could completely break down a thin layer of low-quality plastic within six weeks. Structural biologist John McGeehan and his team have now taken that enzyme and genetically engineered it so that it can begin the process in a matter of days. That kind of discovery is cause for excitement: It takes centuries for polyester, scientifically known as polyethylene terephthalate or PET, to degrade naturally.

John McGeehan at the University of Portsmouth was studying the structure of an plastic-eating enzyme, but ended up engineering it to be much more efficient. (Stuart McDill/Reuters)

All this is just the beginning, though. McGeehan told the Guardian that his team wants to speed up the process even more, and find ways to scale it for industrial use. More importantly, the team imagines that the research can help prevent more plastic from entering the market in the first place.

“What we are hoping to do is use this enzyme to turn this plastic back into its original components, so we can literally recycle it back to plastic,” McGeehan told the Guardian. To grasp what that would mean for the environment, just consider this startling statistic: 1 million plastic bottles are produced each minute. Roughly 10 percent of that gets recycled; the rest ends up in landfills, oceans, and parks.

What is recycled often gets used in textiles, like clothes and carpets. Very few actually become bottles again. So, in theory, if McGeehan’s accidental discovery proves successful, the world could see a future in which we no longer need to dig up more oil to make plastic bottles.

His team wouldn’t be the first to tackle plastic pollution with science. Mother nature, for one, has found her own way to respond… in the form of plastic-eating worms. Last year, researchers in Spain found a species of waxworm that has evolved to not just chew through the plastic bag containing them, but actually eat their way out. They confirmed their hunch by making worm paste, as Ed Yong explained in The Atlantic:

[Biologist Federica] Bertocchini mushed them up and applied the resulting paste to polyethylene. After half a day, around 13 percent of the plastic had disappeared. Even a waxworm smoothie can destroy polyethylene.

The secret was in the worms’ ability to break down beeswax, which contains some of the same chemical bonds found in polyethylene. Since then, researchers have been working to harness the enzymes found in their digestive system in hopes that it can degrade the millions of tons of plastic in our landfills and oceans. Exactly how remains hazy, though one idea that’s been floated is to spray the piles of trash in the ocean with the bacteria or the enzyme, and let them do their work.

Not all researchers see these discoveries, however revolutionary, as the answer to the global pollution crisis. First, there’s the question about practicality, said Susan Selke, the director of packaging at Michigan State University and an engineer who studies plastic recycling. ”Ideally you’d want a whole collection of PET together so you can effectively apply the enzyme—you’re not going to want to spray it over the whole planet,” she said. “And if you’re collecting the PET with the idea of degrading it, you’d be a whole lot better off recycling it instead.”

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She added that PET generally has more value as a recycled material than it does broken down into water and carbon dioxide, which is generally the goal of biodegradation. The bacteria McGeehan worked with breaks plastic into its raw materials (ethylene glycol and terephthalic acid); if the goal is to use those materials to make new bottles, Selke said technology for that already exists.

“We have a substantial number of physical recycling processes that can recycle PET into a food-grade, or FDA-cleared, material, and that is used in producing clear plastic bottles,” she told CityLab. “And if we eliminate the direct food contact restriction, we’ve had technology to produce clear plastic bottles from clear plastic bottles for probably a couple of decades.”

In the grand scheme of things, Selke says, technological innovation is important, but the more fundamental issue is how waste is handled. Even in the United States, not all cities make recycling mandatory. For many, recycling is just too costly and perhaps not worth it. The calls for recycling are even more bleak outside the U.S., particularly in low-income countries where the task falls on informal waste collectors who are underpaid and under-appreciated

Of course, like nearly all environmental problems, plastic pollution has several dimensions and needs to be tackled from all angles. If the history of scientific breakthroughs is any indication, the accidental discoveries of super enzymes and plastic-eatingworms may, at the very least, leave a footprint in our ongoing battle to save the Earth from waste.

About the Author

Linda Poon is a staff writer atCityLab covering science and urban technology, including smart cities and climate change. She previously covered global health and development for NPR’s Goats and Soda blog.

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